Hundreds of passengers were evacuated from Singapore's Changi Airport after a small fire erupted in a terminal that was later extinguished, authorities and witnesses said, delaying flights at the global hub.

Smoke swept through the airport's Terminal 2 building after a fire broke out in the departure hall, spurring authorities to seal off the area.

Three people were sent to hospital for smoke inhalation, the Singapore Civil Defence Force (SCDF) said on its Facebook page.

"A small fire occurred at the departure hall of Changi Airport Terminal 2. The fire has been extinguished by SCDF," the Singapore Police said in a statement.

Police said the fire alarm was activated at around 5:40pm as smoke poured from air vents, sparking an evacuation order and closure of the terminal.